Working conditions of a copper cathode with minimum erosion

Essiptchouk, A. M.; Sharakhovsky, L. I.; Marotta, A.

doi:10.1088/0963-0252/12/4/301

Cited by 14 publications

(3 citation statements)

References 14 publications

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“…Then they employed a theoretical analysis to generate diagrams for the prediction of the best conditions for an arc heater to work with the minimum erosion level. In their following experiments [23], the magnetic field was demonstrated as an important factor in the plasma torch operation, which could significantly reduce the erosion rate.…”

Section: Introductionmentioning

confidence: 99%

Experimental study on copper cathode erosion rate and rotational velocity of magnetically driven arcs in a well-type cathode non-transferred plasma torch operating in air

Chau

Hsu

Lin

et al. 2007

J. Phys. D: Appl. Phys.

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The cathode erosion rate, arc root velocity and output power of a well-type cathode (WTC), non-transferred plasma torch operating in air are studied experimentally in this paper. An external solenoid to generate a magnetically driven arc and a circular swirler to produce a vortex flow structure are equipped in the studied torch system, which is designed to reduce the erosion rate at the cathode. A least square technique is applied to correlate the system parameters, i.e. current, axial magnetic field and mass flow rate, with the cathode erosion rate, arc root velocity and system power output. In the studied WTC torch system, the cathode erosion has a major thermal erosion component and a minor component due to the ion-bombardment effect. The cathode erosion increases with the increase of current due to the enhancement in both Joule heating and ion bombardment. The axial magnetic field can significantly reduce the cathode erosion by reducing the thermal loading of cathode materials at the arc root and improving the heat transfer to gas near the cathode. But, the rise in the mass flow rate leads to the deterioration of erosion, since the ion-bombardment effect prevails over the convective cooling at the cathode. The most dominant system parameter to influence the arc root velocity is the axial magnetic field, which is mainly contributed to the magnetic force driving the arc. The growth in current has a negative impact on increasing the arc root velocity, because the friction force acting at the spot due to a severe molten condition becomes the dominant component counteracting the magnetic force. The mass flow rate also suppresses the arc root velocity, as a result of which the arc root moves in the direction against that of the swirled working gas. All system parameters such as current, magnetic field and gas flow rate increase with the increase in the torch output power. The experimental evidences suggest that the axial magnetic field is the most important parameter to operate the straight-polarity WTC plasma torch at high output power with a limited cathode erosion rate. This emphasizes the importance of an external magnetic field on a WTC torch system for reducing the erosion at the cathode.

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Section: Introductionmentioning

confidence: 99%

Experimental study on copper cathode erosion rate and rotational velocity of magnetically driven arcs in a well-type cathode non-transferred plasma torch operating in air

Chau

Hsu

Lin

et al. 2007

J. Phys. D: Appl. Phys.

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“…ABB Corporation developed vacuum interrupters with self-induced radial magnetic field and up to 100 kA short circuit current. Arc heaters for metallurgical and chemical processes, 28 operating at atmospheric pressure, also employ magnetic field for arc motion, though at quite lower currents ͑up to 1 kA͒. A linear rail geometry for vacuum interrupter was investigated in Ref.…”

Section: ͑4͒mentioning

confidence: 99%

Three-electrode gas switches with electrodynamical acceleration of a discharge channel

Kovalchuk

Kim

Kharlov

et al. 2008

Review of Scientific Instruments

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High voltage, high current, and high Coulomb transfer closing switches are required for many high power pulsed systems. There are a few alternatives for closing switches, for example, ignitrons, vacuum switches, solid-state switches, high pressure gas switches (spark gaps), and some others. The most popular closing switches up to date are spark gaps due to relatively simple design, robustness, easily field maintenance, and repair. Main drawback of spark gaps is limited lifetime, which is related directly or indirectly to erosion of the electrodes. Multichannel switches and switches with moving arc have been proposed to prevent the electrodes erosion. This study investigates switches, where a spark channel is initiated in a three-electrode layout and then the spark accelerates due to electrodynamic force and moves along the extended electrodes. At a given current amplitude, the diameter of the extended electrodes allows to control the spark velocity and hence, the erosion of the electrodes providing the required lifetime. The first switch is designed for 24 kV charging voltage and approximately 4 C total charge transfer. This spark gap was tested at 25 kA peak current in 40 000 shots in a single polarity discharge and in 20 000 shots in bipolar discharge. Second spark gap is designed for 24 kV charging voltage and approximately 70 C total charge transfer. It was tested in 22 000 shots, at a current of 250 kA with a pulse length of 360 mus. In this paper, we present design of these spark gaps and trigger generator, describe the test bed, and present the results of the tests.

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“…The latter is determined primarily by the energy parameters of the arc spot and the character of heat exchange between the electrode and the arc plasma. This heat exchange substantially depends on the method of movement of the arc on the electrode -either with a magnetic field or a vortex gas flow [14][15][16].…”

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confidence: 99%

Investigation of the parameters of a nonstationary arc spot on a copper cathode by the thermospectroscopic method. I. Current density

Bublievskii

Marotta

Esipchuk

et al. 2005

J Eng Phys Thermophys

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A new procedure of determination of the effective density of the current in a nonstationary arc spot with the use of thermophysical and spectroscopic measurements has been proposed and tested. The procedure is based on recording of the critical cathode temperature corresponding to the instant of sharp increase in the intensity of the CuI λ = 5218 A° atomic spectral line, which coincides with the beginning of intense emission of a copper vapor from the spot, according the hypothesis proposed. New results are compared to those obtained earlier by purely thermophysical methods.Introduction. The density of the current in an arc spot is one of the most important parameters determining the erosion and service life of the electrodes in electric-arc gas heaters (EAHs) and other arc devices. One traditionally calculates it from the data of measurements of the current and the dimensions of the arc spot, taking the symmetry of the latter to be circular, i.e., j = 4I/πd 2 . Two methods are usually used to measure the diameter: those of autographs and high-speed photorecording. In the autograph method, the dimension of the emitting region of the spot is taken to correspond to the size of the craters left by it, whereas in the method of high-speed recording, it is taken to correspond to the dimensions of the luminous region of the cathode plasma [1, 2].As has been revealed with the modern technique of optoelectronic recording with a high temporal and spatial resolution, the arc spot on a cold cathode has a very dynamic structure and consists of a large number of individual short-lived microspots that have a complex hierarchic structure and are in continuous motion. Moreover, as the recording technique is improved, this hierarchy increasingly expands toward revealing the finest details of the internal microstructure. Such a situation makes determination of the current-conducting zone of the spot very difficult and dependent on how the situation observed corresponds to the dimension of the zone [2]. In [3], an attempt was made to measure the average dimension of this zone by moving the spot slowly through an insulating gap of a special current sensor divided by this gap into two halves in recording a change in the current in each half. However, the presence of such a gap can substantially distort the shape and dimensions of the conducting zone; therefore, this method applies only to specific conditions of slowly moving spots with a size much larger than the gap size, because of which Szente et al. used it for a plasma cutting arc. In [4,5], traversal of a special linear magnetic sensor by the spot instead of the traversal of an insulated slot was used for such measurements in an electric-arc unit with a magnetic movement of the arc, which introduced no disturbances into the spot itself. However, such a method gives only the linear current density, which is difficult to convert to the real one without knowing the spatial current distribution. Therefore, we proposed that the concept of the effective current density in the arc spot...

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Working conditions of a copper cathode with minimum erosion

Cited by 14 publications

References 14 publications

Experimental study on copper cathode erosion rate and rotational velocity of magnetically driven arcs in a well-type cathode non-transferred plasma torch operating in air

Experimental study on copper cathode erosion rate and rotational velocity of magnetically driven arcs in a well-type cathode non-transferred plasma torch operating in air

Three-electrode gas switches with electrodynamical acceleration of a discharge channel

Investigation of the parameters of a nonstationary arc spot on a copper cathode by the thermospectroscopic method. I. Current density

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